Dr. Alice Roberts embarks on a quest to discover what lies behind the passion for wild swimming, now becoming popular in Britain. She follows in the wake of "Waterlog", the classic swimming text by journalist and author Roger Deakin. Her journey takes in cavernous plunge pools, languid rivers and unfathomable underground lakes, as well as a skinny dip in a moorland pool. Along the way Alice becomes aware that she is not alone on her watery journey.